Vitamin D may improve survival rates for patients with some types of advanced cancer, according to new research presented this week at the 2015 American Society of Cancer Oncology (ASCO) Gastrointestinal Cancers Symposium in San Francisco. The study, led by researchers at Dana-Farber Cancer Institute, found that clinical trial patients with metastatic colorectal cancer who had high levels of vitamin D in their bloodstream prior to treatment with chemotherapy and targeted drugs survived longer, on average, than patients with lower levels of the vitamin.

The research, based on data from more than 1,000 patients with metastatic colorectal cancer who enrolled in a phase 3 clinical trial of chemotherapy plus biologic therapies, adds to vitamin D’s already impressive luster as a potential cancer-inhibiting agent. In the study, patients with the highest blood levels of vitamin D survived for a median period of 32.6 months, compared to 24.5 months for those with the lowest levels.

“This is the largest study that has been undertaken of metastatic colorectal cancer patients and vitamin D,” said the study’s lead author, Dr. Kimmie Ng, MD, MPH, a medical oncologist at Dana-Farber. “It’s further supportive of the potential benefits of maintaining sufficient levels of vitamin D in improving patient survival times.”

Vitamin D is a fat-soluble vitamin found in certain foods, such as oily fish. However, the body’s main source of vitamin D is from the sun. Vitamin D is also the only vitamin that is a hormone. After it is consumed in the diet or absorbed (synthesized) in the skin, vitamin D is then transported to the liver and kidneys where it is converted to its active hormone form.

Survival time was 33% longer among patients with highest levels of vitamin D

To reach their conclusions, researchers measured blood levels of 25-hydroxyvitamin D, a substance produced in the liver from vitamin D, in 1,043 patients when they enrolled in a phase 3 trial of three different drug combinations for newly diagnosed, advanced colorectal cancer. Patient vitamin D levels ranged from an average of 8 nanograms/milliliter (ng/mL) in the lowest group to an average of 27.5 ng/mL in the highest group. The average level in all the patients was 17.2 ng/mL. Current practice guidelines from the Endocrine Society define vitamin D deficiency as having less than 20 ng/mL.

Researchers divided the patients into five groups based on vitamin D levels. On average, those with the highest levels survived 33 percent longer than those with the lowest (32.6 months vs. 24.5 months). Additionally, higher vitamin D levels were also associated with longer time to disease progression — an average 12.2 months in patients with the highest levels compared with about 10 months in the group with the lowest. There were no significant differences with regard to the type of therapy the patients received.

Because high vitamin D levels can be a reflection of a healthy lifestyle (good nutrition, plenty of outdoor physical activity), researchers controlled for factors such as diet, obesity, and level of physical activity. Even then, the relationship between elevated vitamin D levels and extended survival held firm, Dr. Ng observed.

The study didn’t examine whether there is a biological cause-and-effect relationship between higher vitamin D levels and extended survival. As a result, researchers said, it’s too early to recommend vitamin D as a treatment for colon cancer. Dr. Ng and colleagues at Dana-Farber are conducting clinical trials to further investigate whether vitamin D supplementation is useful in treating the cancer. Other remaining questions include when to start taking vitamin D, what dose to take, and for how long, to potentially see a benefit.

In addition to its cancer-fighting properties, vitamin D also plays a key role in the development of strong muscles, bones, and teeth, and is necessary for optimal brain functioning. In fact, recent research suggests that vitamin D deficiency may increase the risk of brain disorders such as dementia and schizophrenia.